One of the most important industrial processes for the production of hydrogen peroxide is the so-called anthraquinone process.
As is known in this process there is employed an alkyl anthraquinone as the reaction carrier, it is hydrogenated in the presence of a catalyst and the anthrahydroquinone formed subsequently is again oxidized whereby both the originally employed anthraquinone is recovered and simultaneously hydrogen peroxide also is obtained. The latter is generally removed from the process of production by extraction with water.
In order to carry out the process both the anthraquinone and the anthrahydroquinone formed in the process must be present in dissolved form. The totality of anthraquinone, anthrahydroquinone and the solvent, as is known, is the so-called "working solution".
The high requirements which are placed on the solvent in the anthraquinone process are generally fulfilled industrially only by mixtures which are so composed that they contain at least one solvent that preferably dissolves the quinone form of the reaction carrier and at least one solvent that preferably dissolves the hydroquinone form of the reaction carrier. As is known these solvents are designated according to their function as quinone or hydroquinone solvent.
Working solutions which consist of only one solvent could not previously be carried through industrially, see Winnacker-Kuchler, Chem. Technologie, Vol. 1, Anorg. Technologie I, 1970 pages 533 and 534. Several of the solvent mixtures proposed in the patent literature are collected in Table 1.
TABLE 1 ______________________________________ German Patent or Hydroquinone Auslegenschrift Quinone Dissolver Dissolver 963150 benzene methyl cyclohexyl acetate 953790 alkylbenzene methyl cyclohexyl acetate 888840 methyl napthalene diisobutyl carbinol 1019290 methyl napthalene phosphoric acid esters 1261838 alkylbenzene phosphoric acid esters 1945750 ter. butyl benzene phosphoric or phosphonic acid esters 2018686 aromatic hydrocarbons tetralkyl, cyclo- alkyl or aralkyl substituted urea ______________________________________
Giesselmann U.S. Pat. No. 3,767,778 corresponds to German Pat. No. 2018686. The entire disclosure of the Giesselmann U.S. patent is hereby incorporated by reference and relied upon.
Furthermore it is known to employ mixtures of hydroquinone solvents in addition to the quinone solvent; thus there is used according to the process of German Pat. No. 2532819 as the quinone solvent an aromatic hydrocarbon, as the hydroquinone solvent to use as the hydroquinone solvent a mixture of a tetraalkyl, cycloalkyl or aralkyl urea and a trioctyl phosphate or phosphonate. Giesselmann U.S. Pat. No. 3,819,818 corresponds to German AS 2125 159 and discloses mixtures of a substituted urea and a triaryl phosphate or phosphonate in the anthraquinone process. The entire disclosure of the Giesselmann U.S. Pat. No. 3,819,818 is hereby incorporated by reference and relied upon.
In the industrial utilization of the anthraquinone process, as has been said, the working solutions and therewith the solvents contained therein according to the cyclic carrying out of the process are supplied both to the reduction step in which the solvent in the presence of noble metal catalyst is subject to the attack of hydrogen as well as to the oxidation step in which generally at higher pressure the solvents are exposed to the attack of oxygen.
The solvents for the quinone and hydroquinone thus must not only be good solvents for the quinone or hydroquinone form of the reaction carrier but they must also be changed at little as possible in the hydrogenation and oxidation steps, besides have little solubility in water and aqueous hydrogen peroxide solutions but have such a density that in the extraction of the hydrogen peroxide with water separation of the two phases is possible without doing anything special. Furthermore they should have a low volatility but a high distribution coefficient for hydrogen peroxide in the system solvent/water and besides have as low as toxicity as possible, see Ullmann, Enzyklopadie der technischen Chemie, 4th edition, Vol. 17, page 698. Besides they should give a high yield of hydrogen peroxide.
However, previously it has proven quite difficult to obtain a substantial resistance of the solvent, i.e. a substantial avoidance of breakdown products, in the individual process steps. This was particularly difficult in the oxidation step.
In German AS 1945750 for the first time there was proposed an oxidation resistant quinone solvent, namely tert. butyl benzene.
Hereby there was designated as "oxidation resistant" in the anthraquinone process a solvent which withstood the attack of oxygen without noticable change at 140.degree. C. for several hours, i.e. about 1.5 to 48 hours.
In German AS 1914739 indeed there are mentioned solvents which are oxidation resistant against molecular oxygen, whose yield of hydrogen peroxide however is extremely low compared to the process of German Pat. No. 2018686 (or related Giesselmann U.S. Pat. No. 3,767,778).
Therefore there have been used in order to have both a sufficient oxidation resistance and yield of hydrogen peroxide the quinone solvent together with specific antioxidants, so e.g. German Pat. No. 2104432 and related Giesselmann U.S. Pat. No. 3,789,114,. The entire disclosure of Giesselmann U.S. Pat. No. 3,789,114 is hereby incorporated by reference and relied upon.
The purpose of the present invention therefore is the use of an oxidation resistant solvent in the anthraquinone process which simultaneously guarantees a high yield of hydrogen peroxide.